The present invention relates to a device for preventing the electrical shorting of a stack of electrolytic cells during an extended period of operation. The device has application to fuel cell and other electrolytic cell stacks operating in low or high temperature corrosive environments. It is of particular importance for use in a stack of fuel cells operating with molten metal carbonate electrolyte for the production of electric power. Also, the device may have application in similar technology involving stacks of electrolytic cells for electrolysis to decompose chemical compounds. A representative fuel cell stack is illustrated in U.S. Pat. No, 4,345,009, Aug. 17, 1982.
The individual stacks of cells must be provided with reactant gases for their operation. Fuel gases such as hydrogen or producer gas from the gasification of solid carbonaceous material can be employed at the negative electrodes in a fuel cell stack. In addition, an oxidant gas such as oxygen or air is provided for reaction at the positive electrode. In cells employing metal carbonate electrolyte, carbon dioxide generated in the negative electrode is provided to the positive electrode for replenishing carbonate in the electrolyte.
The manifolds carrying these reactant gases must be connected to the cell stacks in an electrically insulated and leak type manner. The high temperature and corrosive environment in molten carbonate and other types of cell stacks have resulted in only a select few types of sealing designs to connect the manifolds to the stacks. One such design is described in U.S. Pat. No. 4,414,294 issued to Guthrie, Nov. 8, 1983. The disclosure of this patent is specifically incorporated by reference herein for the purpose of describing a sealing arrangement between the gas supply manifold and fuel cell stack.
In addition to the difficult problems of sealing the manifold to the stack, long term operation has resulted in the electrical shorting of groups of cells within the series arranged stack. These electrode shorts were believed to be the results of corrosion products from the fuel cell stack structure. Previous attempts to correct this problem have involved the selection of less corrosive construction material or coatings on materials exposed to the high temperatures and corrosive electrolyte. Such an approach is not totally effective and is expected to result in substantially increased cost of cell stack construction.